In cell initial search of the LTE, it needs to demodulate a public broadcast channel (P-BCH) to obtain configuration information of the cell. The steps of demodulating the P-BCH generally include: channel estimation, multi-input multi-output (MIMO) receiving, convolutional codes decoding and cyclic redundancy check (CRC), etc. Since the P-BCH adopts a transmit diversity scheme, the number of transmitting antenna ports of a base station has three possible configurations: 1, 2, and 4 antenna ports. However, this information is unknown to a UE, the UE has to try all the three possible modes of transmit diversity schemes, and determines the transmit diversity scheme used by the base station according to the CRC in the demodulated P-BCH information.
In this way, the receiver needs to detect the P-BCH for three times at most in order to obtain the correct transmit diversity scheme, and the more times for detection is, the more power consumption of the UE is. Moreover, since the process of three demodulations needs to be performed possibly within one transmission time interval (TTI) of the P-BCH, the requirement on the detection speed is also raised by three times.
In addition, the LTE system supports six different bandwidths: 20M, 15M, 10M, 5M, 3M and 1.4M, and the UE with one bandwidth needs to support narrow-band working modes, for example, a UE with a maximum bandwidth of 20M can work in a 10M or 5M mode. When the cell initial search is performed, P-BCH signals are present in 1.4M at the middle of a frequency band, a bandwidth configuration of a transmitter can be known only after P-BCH demodulation, which means that the UE can only use the information in the bandwidth of 1.4M to perform the P-BCH demodulation. If the UE can know the system bandwidth in advance, for example, 5M or more, the UE can use information in more bandwidths. For example, the channel estimation needs to use reference signal (RS), and more RSs can be detected in the bandwidth of 5M, so this is very helpful to the performance of the channel estimation.
As mentioned above, in the cell initial search, the receiver needs to perform multiple demodulations on the P-BCH to obtain the number of the transmitting antenna ports, thus reducing the performance of the cell initial search and increasing the complexity of calculation when the receiver performs the modulation.